In a conventional core monitoring system for a nuclear plant, a TIP (Traversing Incore Probe) device is used about once every month to measure an amount of neutron while moving a detector inside a reactor in an axial direction thereof. And data of a reactor power distribution at each height position in a core axial direction are transmitted to a process computer. The process computer uses the data to maintain accuracy of the power distribution calculation performed every stipulated time period.
A conventional core monitoring system is illustrated in FIG. 7 (Patent Documents 1 and 2). In FIG. 7, a TIP device drives a TIP detector 1-4 in TIP guide tubes 1-3 installed inside a core 1-2 of a reactor 1-1 to generate a TIP position signal corresponding to a travel distance when pulling the TIP detector 1-4 from the core top toward the core bottom, and reads a TIP level signal in synchronization with the TIP position signal to thereby measure neutron distribution along axial direction of the core.
The TIP detector 1-4 is driven based on a drive signal (detector insertion/pull-out signal) that a process computer A and a TIP panel C output, while cooperating with each other, to a TIP drive device D.
Along with loading of TIP position signal 5 and TIP level signal 6, the process computer A reads an LPRM (Local Power Range Monitoring) level signal and an APRM (Average Power Range Monitor) level signal from a neutron monitoring panel B at a predetermined timing to increase accuracy of a power distribution calculation performed in a core performance calculation or LPRM/APRM gain calibration.
Further, the process computer A inputs thereto from the TIP device the TIP position signal 5 indicating a height position of the TIP detector and the TIP level signal 6 corresponding to the height position, and a time [ms] when the above signals are obtained and inputs thereto from the neutron monitoring panel B the LPRM level signal and the APRM level signal 7, plant data (feed water flow rate, pressure, temperature, etc.) and control rod position data required for heat balance calculation or power distribution calculation which are to be calculated in the core performance calculation.